In recent years, the “cumene method” has become the basis for the core technology utilized in the majority of commercial processes for phenol production. Typically, the cumene method includes chemical stages of isopropyl benzene (cumene) oxidation into cumene hydroperoxide (CHP), and further decomposition into phenol and acetone (with the use of acidic catalyst). Chemical characteristics of phenol production process by cumene method determine the contents of a number of chemical compounds being generated as byproducts and appearing in the end product as impurities.
The most common impurities which deteriorate the desirable application properties of end-materials produced at successive phenol processing stages are alkylaromatic, unsaturated and carbonyl-containing compounds, such as alpha-methyl styrene (AMS), mesityl oxide (MO), phorone, 2-methylbenzofuran (2-MBF), hydroxyacetone (HA), cresols, and so on. By way of example, the following reactions describe several possible ways in which undesirable impurities may form during phenol production, as well as illustrate the directions taken by further conversion reactions:

Phenol used in the production of pharmaceuticals and certain polymeric materials must meet high standards with respect to maximum permitted impurity content, which typically does not exceed 0.0100 wt. %. Naturally, such applications require special methods of phenol treatment to eliminate or substantially reduce the presence of undesirable materials in the final phenol product (i.e., impurities, etc.).
Previously known existing approaches to phenol treatment are directed to physical and chemical methods. Physical methods of separation of unwanted compounds commonly encompass fractionation, azeotropic rectification, and extraction, for example as discussed in U.S. Pat. Nos. 2,744,144; 4,532,012; 3,405,038; and 4,504,364.
The main disadvantages of physical methods of phenol treatment, which are widely used in commercial production, are very high energy consumption, and increased sensitivity to volumetric feed rate: increasing of feed rate over a previously established design rate, has an adverse impact on phenol quality.
A vast number of applied chemical methods of phenol treatment are also known. Typically, they are directed to methodologies which rely on chemical properties of compounds which pollute phenol. The most common widely used chemical methods of impurity removal from phenol are demonstrated in the above-shown chemical reactions, with successive rectification-based separation of condensation products (formed during reactions) from phenol. Homogeneous acidic catalysts (for example, see U.S. Pat. No. 3,810,946) and alkaline catalysts (for example, see U.S. Pat. No. 3,335,070) are generally used as catalysts to assist in the reactions.
Another phenol treatment method has been proposed which, together with phenol treatment with alkali (of a pH value reaching 7-9), also uses oxidation by air oxygen (for example, see European Patent No. 1,188,477, and U.S. Pat. No. 3,862,244).
Some of the previously known methods of impurities removal are focused on specific chemical compounds, which have an significant negative impact ion various important quality factors of phenol. Various methods of HA removal serve as an example of this approach. When HA and MBF are derived from phenol using conventional approaches, they impair the color of the phenol product and phenol-based plastic masses. Since it is very important to ensure a required color index, other special methods with different approaches to the solution of the problem have been sought.
The majority of these traditional special methods are based on removal of impurities of HA and MBF from the phenol stream, in which they are accumulated at a CHP cleavage products fractionation stage. This is accomplished by the abovementioned physical methods of aqueous-extractive distillation and extraction, as well as by various chemical methods. In particular, one method of removal of HA from phenol, that consists of conversion of HA into heavy nitrogenous compounds by adding high-molecular amines, is described in U.S. Pat. Nos. 3,322,651 and 3,692,845.
The main disadvantages of these methods are a high cost of amines, as well as the problems with nitrogenous compounds waste treatment, which carries an adverse environmental impact.
The U.S. Pat. No. 6,066,767 introduced a completely different approach to ensure that the required phenol color index is met at the output, is based on the avoidance of MBF formation at a fractionation stage by means of prior removal of HA from CHP cleavage products by circulating salt aqueous solutions. Within this method, the conversion of the extracted HA and aldehydes into the products of deep condensation at pH value more than 7 is conducted in a separately installed reactor, at a temperature of not higher than 130° C. This method is effective for HA (and therefore MBF) removal, but it requires a multi-step extraction and is capital- and energy-intensive.
Another method, described in U.S. Pat. No. 6,573,408, adopts the '767 Patent approach to HA removal, but it has only a single extraction step at a pH value of 3-6, and the temperature of the aqueous salt solution treatment is increased to 300° C. However, these changes only decrease a degree of extraction of HA from CHP cleavage products and boosts energy consumption of the process so dramatically, that this method becomes economically unjustified.
A method of oxidative (air) conversion of HA was proposed in the Oil Refining and Petrochemistry publication ((Russia), 2000, Issue 12, P. 507-510), and allows substantial savings on investments in the processes based on HA extraction, and further conversion in aqueous salt solution. HA oxidation with the use of an alkaline catalyst, proceeds at a rate approximately 10 times higher than its condensation reaction rates, which makes it possible to reduce the reactor size proportionally. The requirement of multi-step extraction for the full HA removal remains a key disadvantage of this method.
Yet another method of HA removal, disclosed in U.S. Pat. No. 6,576,798 ineffectively combines the known techniques of HA removal by aqueous salt solution (as taught in U.S. Pat. No. 6,066,767), with the use of oxidation for HA conversion in this media (see Oil Refining and Petrochemistry (Russia), 2000, Issue 12, P. 507-510)), where hydrogen peroxide, its salts, and permanganates of alkali metals are recommended to be used as oxidants at pH of 3-6.
It is known that in extraction, phenol and acetone enter the aqueous salt solution together with HA, with the concentration of phenol and acetone being about 10 times higher than the HA content. Accordingly, 96-97% (relat.) of the inorganic oxidant injected into the reactor, is spent for oxidation of these target products, boosting the consumption of expensive materials, and leading to unreasonably high expenses.
The most widely used method in commercial production is phenol treatment from impurities with the use of heterogeneous acidic catalysts, mainly sulfonic ion-exchange resins. An obvious advantage of this method over the ones based on the direct use of acids or alkalis, is that it proceeds without waste water formation. However, the use of sulfo-IER as treatment catalysts has its shortcomings. These catalysts are polymeric materials characterized by low mechanical strength and thermostability. In addition, they are prone to swelling and decrepitating at operation. Also, phenol treatment sulfo-IER catalysts have a limited life time, cannot be regenerated, and must be burned in special incinerators after discharge.
The closest counterpart of this approach, is a method of treating phenol from carbonyl containing and unsaturated compounds which involves the contacting of phenol with zeolite catalyst, i.e. mineral catalysts, for example, promoted aluminosilicates with a pore diameter of over 4 Angstrom, at atmospheric pressure or a pressure at which phenol is in liquid phase, and at a temperature of 120° C. to 250° C. These catalysts have no temperature limits for the considered process, are mechanically strong and can be regenerated by air oxygen with restoration of the initial properties. Unfortunately, zeolite catalysts are not universal in respect of treatment of the whole range of impurities contained in phenol. For example, the treatment of phenol from MO and AMS is quite effective, while MBF is not convertible with the use of zeolite catalysts. Moreover, although HA is contained in phenol as an impurity, it is fully convertible in the presence of zeolite catalyst—its disappearance is followed by MBF formation from HA and phenol interaction.